unit 4 reproduction · pdf fileunit 4. reproduction . 1. ... sexual reproduction in flowering...

UNIT 4. REPRODUCTION

1. LIFE CYCLE

http://www.edistribucion.es/anayaeducacion/8430042/UNIT_4/unit_04_video_01.html

� The life cycle of an organism is the stages which it

passes through during its life.

� Living beings go through several different stages

during its life:

� First it is born

� Next it develops and grows to become an adult

� Then it reproduces to produce offspring

1. WHAT IS REPRODUCTION?

� Reproduction is the biological process by which

new individual organisms (offspring) are produced.

� It ensures the perpetuation

of the species.

� Progenitors are able to

multiply and generate new

living beings, descendants.


� There are two main types of reproduction:

� Asexual reproduction: a single individual is able to separate a part of its

body and this develops into a new being. The descendants are genetically identical to the progenitors. To reproduce the living being need the right environmental conditions and enough food. The advantage is that one parent can produce a lot of offspring, so the population can increase rapidly. Asexual reproduction happen in algae, protozoa, fungi and some plants and animals


� Sexual reproduction: two individuals (male + female) are necessary. Each one makes different special cells: the gametes, which join together and became a single cell a zygote, by means of fertilisation. The descendants have a combination of genetic material contributed from both parents. To reproduce two organisms need to find each other. Also one type of gamete need to be able to move easily, and the gametes need to be in a liquid for carry out fertilisation and a lot of resources are needed to produce gametes and develop the embryo. The advantage is that organisms are more diverse, so they are better at adapting to changes in their environment. Sexual reproduction happens in plants and most animals.

2. ASEXUAL REPRODUCTION IN ANIMALS

� It only occurs in the most simple and least evolved animals.

� Types:

GEMMATION FRAGMENTATION

- An outgrowth, bud, from the body of

the parent, develops into a new

individual.

- Hydra, coral (colony)

- A new organism grows from a fragment

of the parent. Each fragment develops

into a fully grown individual.

- Planaria worm, starfish


2. ASEXUAL REPRODUCTION IN ANIMALS

� GEMMATION

� FRAGMENTATION

3. SEXUAL REPRODUCTION IN ANIMALS.

� Sexual reproduction in animals usually requires two members of the opposite sex, a male and a female.

� Each member has different reproductive organs called gonads . The male gonads are the testicles and the female gonads are the ovaries.

� These organs make reproductive cells called gametes . The male gamete is called spermatozoon (they are very small and they can move easily) and the female gamete is called egg or ovum (they are much bigger than sperm because they contain nutrients)


� Depending on the type of gonad present, animal can be:

� Unisexual: Each individual has only one type of gonad. Most

animals are unisexual.

� Hermaphrodite: Each individual has both male and female gonads. Examples of hermaphrodites: snails and slugs, as well as some types of worms, molluscs, crustaceans and fish. (Normally they don´t fertilise themselves, they still need two parents to produce offspring. One parent acts as the male and the other acts as the female)


� UNISEXUAL:

� In certain species of animals, the two

sexes differ only in their sexual

organs. Examples are rabbits, cats,

dogs, etc.

� In other species, in addition to

having different reproductive organs,

females and males are very different

in their appearance: these species

exhibit sexual dimorphism. Examples

of species that display sexual

dimorphism are lizards, lions, many

birds, human beings, etc.

4. WHAT IS FERTILISATION?

� Fertilisation is the union of an ovum and a spermatozoon. When the eggs and spermatozoon join, they form a fertilised egg called a zygote. Initially, the zygote is just one cell, but then the cell divides by mitosis. The cells continue dividing, so there are more and more cells.

� There are two types of fertilisation:

- External fertilisation is the union of the gametes which occurs

outside the female’s body. First, the female releases the

unfertilised eggs. Then, the male releases sperm to fertilise

them. The fertilised eggs then develop into embryos, and

finally, into adult individuals. With external fertilisation, each

egg has low chance of being fertilised, so the animals need to

release large amounts of eggs and sperm. It is typical of aquatic

animals, and some terrestrial ones such as amphibians and

some insects

- Internal fertilisation is the union of the gametes which occurs

inside the body of the female. It involves copulation which is

the transmission of spermatozoon of the male into female. It is

typical of most terrestrial animals and some fish.


4. WHAT IS FERTILISATION?

5. EMBRYONIC DEVELOPMENT

� Embryonic development includes the processes from the formation of the zygote to the birth of the new individual.

� After fertilisation, the zygote undergoes many cellular changes and becomes a developing organism, called an embryo.

� Depending on where embryonic development take place, animals can be classified as:

� Viviparous: The embryo develops inside the female body. The embryo grows inside of uterus. The placenta feeds the embryo through the umbilical cord. Embryonic development ends with birth. Is typical of mammals with placentas, but also of some fish, reptiles and amphibians with placenta-like structures.

� Oviparous: The embryo develops inside an egg ( that contains nutrient to feed the embryo). To start with, the egg is inside the mother, then the mother lays the egg, so the embryo finishes developing outside the mother. Embryonic development ends when the eggs hatches (the baby breaks out of the eggs). This is typical of birds, reptiles and fish.

� Ovoviviparous: The embryo develops inside an egg which remains inside the female’s body until it hatches. The eggs hatch inside the mother, and then the mother gives birth to live offspring. The egg contains nutrients to feed the embryo. This is typical of some sharks, rays, snakes and lizards.

6. POST-EMBRYONIC DEVELOPMENT

� It is the growth of the organism until it reaches the adult state, in which it acquires the ability to reproduce.

� There are two types:

� Direct development: The new-born individual is similar to the adult, only smaller. Its development consists of: growth and maturity of the organs. Animals that receive a lot of nutrient before they are born develop in this way. Examples: mammals, birds, and most types of fish and reptiles.

� Indirect development: Some animals develop less before they are born, because they don´t receive as many nutrient. The offspring has to go through various changes in order to become an adult. These changes are called metamorphoses. Examples: many insects, amphibians and molluscs. There are two types of metamorphosis:

� Incomplete metamorphosis: the offspring that hatch from the eggs are called nymphs. They already look like small adults, but in order to grow they have to moult (change their exoskeleton) several times.

� Complete metamorphosis: The offspring look completely different from the adult. They are called larvae. They have to go through bigger changes to become adults, in which the larva loses some organs and generates others.


� INCOMPLETE METAMORPHOSIS


� COMPLETE METAMORPHOSIS



7. ASEXUAL REPRODUCTION IN PLANTS

� It involves the formation of new individuals from the cells of

a single parent.

� There are two main types:

� Spore formation: The nucleus of the parent cell divides repeatedly into a

number of daughter cells, called spores. These spores become new

individuals without attaching themselves to other cells. Ferns and

mosses reproduce by spores.

7. ASEXUAL REPRODUCTION IN PLANTS

� Vegetative reproduction: Plants create new individuals from a particular

organ, usually from the stem. Types:

� Bulb: is a stem with thick leaves that grows underground. Example: onions, tulips,

garlic…

� Tuber: is an enlarged stem or toot that grows underground. The tuber conains a

store of nutrients that the new plant can use. Example: potatoes

� Stolons or runners: are stem that grow horizontally above the ground. A new plant

can grow from the runner. Example: strawberries, clover, spider plant …

8. SEXUAL REPRODUCTION IN PLANTS

� Sexual reproduction: It is typical of plants with seeds. The

reproductive organs are inside the flower, where gametes

are produced.

� The flower structure consists of the following parts:

� Calyx: is formed of the green sepals which protect the flower.

� Corolla: is formed of the brightly coloured petals. The petals attract

insects to facilitate pollination.

� Stamen: is the male reproductive organ of flower. It consists of filament

and anthers (where the pollen is stored)

� Pistil: is the female reproductive organ of the flower. It consists of

stigma, style and ovary (where the ova are stored)


� The flower structure:

http://www.youtube.com/watch?v=X7zW5W6XGeg


� Sexual reproduction in flowering plant has several stages: pollination,

fertilization, seed dispersal and germination

� Pollination


� Fertilisation


� Seed dispersal


� Germination


� TO SUM UP:

1. The pollen grains land on the pistil helps by wind, insects…(Self -pollination or cross-pollination )

2. Then pollen tubes develop until they reach the ovary, where fertilisation occurs.

3. Inside the ovary the male (pollen) and female (ovum) gametes fuse to form the zygote.

4. The zygote grows into an embryo.

5. The ripened ovule becomes a seed. The seed contains the embryo and food for the new plant (endosperm). The seed feeds the plant until it grows green leaves responsible for photosynthesis.

6. The ripened ovary becomes the fruit (dry fruit or fleshy fruit). It is responsible for protecting and dispersing the seed.

7. Seed germination to develop a new plant.


� TO SUM UP:

unit 4 reproduction · pdf fileunit 4. reproduction . 1. ... sexual reproduction in flowering...

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